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Glycerin is a colorless and odorless fluid obtained from lard, tallow, and other oils, in various quantities. It has a peculiar sweetish taste, whence it has been called the sweet principle of oils. Its specific gravity is 1.260; it remains fluid indefinitely; is miscible with water and alcohol in all proportions; and has a sirupy consistence, and somewhat oily touch.

Glycerin was first obtained during the preparation of lead plaster. In this process, where litharge and olive oil are boiled together in water, the acids of the oil unite with the oxide of lead as a base, when the glycerin is set free and unites with the water. The liquid being decanted, any lead it may contain is separated by sulphuretted hydrogen and nitration, and the water is then evaporated from the glycerin. The same changes are effected when the soap-maker uses potassa and soda (instead of lead) as bases to combine with the margaric and stearic acid of fats–the glycerin being thus again set free in the presence of water, with which it at once mixes. Glycerin thus obtained, however, has a peculiar odor, from which it is scarcely possible to free it; and is not usable except to form certain classes of toilet-soaps. When fats are subjected to a high steam pressure in the presence of a moderate quantity of milk of lime, a lime soap is formed, and the glycerin is set free in a pure form. This is the present method of obtaining all good glycerin. Dr. C. Morfit, as quoted by the U. S. Dispensatory, thus describes the process in Silliman's Journal, (2d series, Vol. XV:) "Melt one hundred pounds of tallow or lard in an iron-bound barrel, by a current of steam; and add to it fifteen pounds of lime made into a milk with two and a half gallons of water. Continue the steam for several hours, till complete saponification takes place. The acids of the oil unite with the lime to form an insoluble soap; and the glycerin remains in the water along with the excess of lime. After the liquid has cooled and settled, it is strained through a crash-cloth; the fluid concentrated carefully by steam heat, and treated with a current of carbonic acid to remove the lime as a carbonate; boiled again, and again allowed to settle. The clear liquid is finally strained off, and concentrated by driving off the water." This process gives a fine quality of glycerin at a low cost; and the lime soap may be treated with very dilute sulphuric acid to release the fats, which are then used for star candles.

Impurities and Tests: Chlorine is sometimes used in bleaching a poor quality of glycerin; and may be detected by making the liquid slightly blue with sulphate of indigo, and adding a little sulphuric acid, when the blue color will disappear if chlorine (more properly chloride of lime) be present. Oxalate of ammonia will detect the least trace of lime by forming an insoluble precipitate; hydrosulphuret of ammonia will make a black precipitate if any lead be present; and a solution of any baryta salt will vield a white cloud with the smallest trace of sulphuric acid.

Properties and Uses: Glycerin is not used internally to any extent as yet; though it has been spoken of as a substitute for cod-liver oil in phthisis. Its chief medicinal value is in external appliances, and as a solvent in various pharmaceutical preparations. It is softening to the skin; and may be used for irritable diseases of the surface, such as eczema, prurigo, lichen, herpes, etc. It has also been used for incrustations, as in lupus and syphilis. It is a popular application for chapped hands and lips. Many times it causes unpleasant stinging when applied to any abraded surface, which may be obviated by dilution with equal parts of water. The purest article is often quite unpleasant to mucous surfaces, as to the vagina; yet dilution will generally obviate this, and it may thus be used in ophthalmia, vaginitis, etc.–either alone, or with suitable medicaments added to it. It also supplies (apparently) the nutriment needed by the hair follicles; and may be used in dandruff and other forms of scurfy disease of the scalp; or medicated with lobelia and a little oak bark for falling off of the hair, for which such a preparation is of great value. Added in moderate quantities to poultices, it keeps them moist and prevents adherence to the surface; and for a similar action, it is used freely on wounds and sores which are to be dressed with lint. It softens dried cerumen in the ear; and has been used in deafness and various affections of the ear connected with dryness of the parts. A very little incorporated in a pill mass, or added to solid extracts, will keep them moist and prevent them from molding.

Glycerin possesses a peculiar and powerful solvent property, and is also an excellent preservative. For both these qualities, it is second only to alcohol, and deserves to come into considerable use. Relaxants macerated in it have too mawkish a taste to be always acceptable; but strong stimulants and bitter tonics–as capsicum, quassia, gentiana, aloes, etc.–have their unpleasantness somewhat covered by it. It acts sufficiently on all such substances, when diluted with its own bulk of water, or even more diluted, and still is thoroughly preservative; and as such dilution reduces the mawkish taste, it is probable that the profession can find much advantage in treating numerous agents with it, instead of using so much alcohol as is now customary. Such a use would be appropriate in treating cinchona, quinia, salicin, santonin, and some other vegetable alkaloids; and it would be an object of interest to inquire experimentally how far it will solve myrrh and other gum resins. Many of the essential oils will dissolve in it readily. It is also highly antiseptic, and preservative of animal tissues; but structures preserved in it become slowly softened.

Pharmaceutical Preparations: In ointments, it may be used to advantage in various combinations. Stiffened to any desirable degree by being heated with finely-powdered starch, (thirty or sixty grains to a fluid ounce,) it may be mixed with sulphur in making sulphur ointment; or triturated with the solid extracts, as of celastrus, lycopus, or hydrastis, when these are to be used in salves. Mr. Ricky proposes the following Glycerin Ointment: Spermaceti, half an ounce; oil of almonds, two fluid ounces; glycerin, one fluid ounce; white wax, a drachm. Melt all but the glycerin, pour into a Wedgewood mortar, add the glycerin, and stir thoroughly till cold. It is useful for chaps and excoriations. (U. S. D.) The Journal of Pharmacy commends a mixture, by weight, of five parts glycerin and four parts yolk of eggs, rubbed in a mortar. It is soft and unctuous, and forms an air-tight and soothing application to abraded surfaces, sore nipples, tetter, and irritated affections of the skin, including erysipelas. It will keep indefinitely, and has the advantage of being easily removed with water. Crusts of vaccine virus may be dissolved in glycerin, and kept indefinitely; though it is not fully settled that the virtues of the vaccine are unaffected. Dr. J. P.Easter, of Highland county, Ohio, called my attention to the use of it in ophthalmia; and I have been highly pleased in a limited use of a strong infusion of hydrastis added to an equal quantity of glycerin, with myrrh or capsicum in quantities to suit the indications.

The Physiomedical Dispensatory, 1869, was written by William Cook, M.D.
It was scanned by Paul Bergner at http://medherb.com

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